Processes for the manufacturing of hydrogen peroxide by the anthraquinone process are known in the art. The anthraquinone process typically comprises the cyclic reduction, oxidation and extraction of a solution containing an anthraquinone derivative. This solution containing the anthraquinone derivative is generally known in the art as “working solution” and it typically comprises a suitable inert solvent, typically an organic solvent, or mixtures thereof. The working solution further comprises at least one anthraquinone derivative, which is hydrogenated into its corresponding anthrahydroquinone derivative and reoxidized in the corresponding anthraquinone derivative during the cyclic anthraquinone process.
In the hydrogenation step, the anthraquinone derivative is reduced to the corresponding anthrahydroquinone derivative, usually by catalytic hydrogenation. In the subsequent oxidation step, the hydrogenated working solution, which is to be freed from the catalyst beforehand, is oxidized, typically by gassing with oxygen or an oxygen containing gas mixture. During oxidation, the anthrahydroquinone derivative is oxidized into the corresponding anthraquinone derivative, whereby hydrogen peroxide is obtained. The working solution containing the oxidized anthraquinone derivative and the hydrogen peroxide is extracted to remove the hydrogen peroxide and is recycled to be reused in the reduction step.
Further details of the anthraquinone process for the manufacture of hydrogen peroxide are disclosed in standard text books, e.g., Kirk-Othmer, Encyclopedia of Chemical Technology, August 2001, Chapter “Hydrogen Peroxide”; or Ullmann's Encyclopedia of Industrial Chemistry, fifth edition, 1989, Volume A 13, pages 449-454.
The oxidation step of the anthraquinone process is known in the art as both energy and solvent consuming. During the oxidation step, the oxidation gas has to be fed into the reactor with sufficient overpressure. The oxidation off gas obtained from the reactor, after sufficient contacting the working solution, is typically still under significant overpressure when leaving the oxidation reactor. Further, typically high amounts of solvents are still present in the oxidation off gas. Several solutions have been proposed in the art to overcome these disadvantages.
U.S. Pat. No. 4,485,084 suggests isentropic expansion of the oxidation off gas from the oxidizer in order to recover the solvent. By isentropic expansion in a turboexpander part of the energy of the overpressure can be recovered.
DE 4029784 suggests conducting the oxidation step with pure oxygen instead of air to avoid the production of oxidation off gas. As pure oxygen is expensive such process is economically very inefficient and therefore not suitable for continuous industrial process, where typically air is used as oxidation gas. The present invention is therefore directed to continuous processes for the manufacture of hydrogen peroxide, where no pure oxygen is applied as oxidizing gas and thus oxidation off gas is produced.
US 2003/0165422 A1 suggests feeding the oxidation off gas as a propellant gas in one or more gas jets (gas ejectors) in order to recover the energy present in the off gas, which is still under pressure.
It has been found that when the oxidation off gas obtained from the oxidation reactor, which is still under overpressure, is used as propellant gas for a gas ejector, the efficiency of the gas ejector is rather low and the ejectors have been found as mechanically unreliable and as causing frequent process off times.